JP2012515129A - Silicon purification method and apparatus - Google Patents

Abstract

Methods and related materials for the production of chlorosilanes (mainly: trichlorosilane) and for the deposition of high purity polysilicon from these chlorosilanes. The source for chlorosilane production is eutectic or hypoeutectic copper-silicon, and the copper-silicon concentration range is 10 to 16 wt% silicon. The eutectic or hypoeutectic copper-silicon is cast into a shape suitable for a chlorination reactor where it is exposed to a process gas consisting at least in part of HCl. This gas reacts on the surface of eutectic or hypoeutectic copper-silicon to extract silicon in the form of volatile chlorosilanes. The deteriorated eutectic or hypoeutectic material can then be recycled, replenished with the extracted amount of silicon, and recast into the desired shape.
[Selection] Figure 1

Description

The present invention relates to a method and apparatus for silicon purification. In particular, the present invention relates to a method and apparatus for the production of chlorosilanes and for the deposition of high purity silicon.

BACKGROUND OF THE INVENTION Metal grade silicon requires prior purification before it can be used in optoelectronic or semiconductor applications. Usually, this process is carried out in several steps which are carried out in succession: In the first step, chlorosilane or monosilane, such as TCS (trichlorosilane SiHCl3), STC (silicon tetrachloride SiCl4), dichlorosilane SiH2Cl2, or Monosilane SiH4 is typically produced in a type of fluidized bed reactor, as described, for example, in US Patent Application Publication No. 2007/0086936 A1. In the next step, the product gas is captured and purified by partial distillation to remove gaseous metal chlorides, BCl3, PCl3, CH4, and the like. High purity chlorosilane is then used as a process gas for the so-called Siemens process, where the silane reacts into silicon and various gas species. The Siemens process is an open loop system, and the process must be continuously supplied with process gas, exhaust gas must be continuously supplemented and treated by special means. This makes the Siemens process somewhat expensive with regard to infrastructure, logistics and labor for exhaust gas treatment. Examples of Siemens methods include US Pat. Nos. 2,999,735; 3,011,877; and 6,221,155, and various textbooks (eg, A. Luque and S. Hegedus (Eds.): “Handbook of Photovoltaic Science and Engineering”, Wiley & Sons Ltd, ISBN 0-471-49196-9).

  Another known approach uses chemical treatment of metal silicon, such as etching and leaching, to remove metal impurities and to reduce the concentration of electrically active elements such as phosphorus and boron. Use with one or more solidification cycles. The final product, upgraded metal silicon (umg-Si) is suitable for photovoltaic applications, but still contains a somewhat higher concentration of impurities.

  Casting silicon with other metals is a known technique for pretreatment of mg-Si in US Pat. No. 4,312,848, where aluminum is used as a solvent for silicon.

  The use of> 20 wt% silicon concentration for copper-silicon as the source material for the production of chlorosilane is described by Olson in US Pat. No. 4,481,232. In Olson, the material was placed in a single chamber compartment. Copper is known not only to act as a catalyst for improving the productivity of chlorosilane production, but also as a getter material for metal impurities. In the Olson patent, copper silicide is placed in the immediate vicinity of the heated graphite filament. The movement of the gas occurs by natural convection caused by the temperature difference between the hot filament and the relatively cool chamber wall. In general, the placement of a single chamber can cause several problems. For example, in the method described in US Pat. No. 4,481,232, only a limited amount of copper silicide can be charged into the chamber, and the alloy is heated indirectly due to its proximity to the filament. . Therefore, the temperature of the alloy cannot be properly controlled and will increase beyond the optimum temperature range for the production of gaseous silicon. Those skilled in the art will note that a temperature that is too high will move the metal impurities trapped in the copper-silicon alloy or in the copper itself, thereby increasing the concentration of metal impurities in the purified silicon. Will recognize. It will be further appreciated that in the presence of hydrogen, too high a reaction temperature will shift the chemical equilibrium towards solid silicon instead of gaseous chlorosilane, thereby reducing productivity. The single chamber configuration also lacks adequate suppression of volatile impurities and particles that would adversely affect the purity of the deposited silicon. It is well known in the silicon industry that even trace amounts of copper are very inconvenient for the use of silicon in semiconductor or solar cell applications.

  As such, the single chamber arrangement disclosed in US Pat. No. 4,481,232 is only suitable for laboratory scale applications and may not be optimal for scale up. A significant disadvantage of the high concentration (eg 20-30 wt% silicon) copper-silicon alloy proposed by Olson is that the alloy tends to oxidize when exposed to the atmosphere, which swells during chlorination. It is to collapse. The latter can be caused by a substantial amount of silicon crystallites and associated cracks scattered in the eutectic copper-silicon alloy.

  High purity silicon is required for any application in the electronics industry, such as the use of solar cells and the manufacture of semiconductor devices. The purity level required for any electronic application is significantly higher than that provided by so-called metal grade silicon (m.g. silicon). This requires a complicated and expensive purification process. This leads to a strong need for a more cost effective and energy efficient process for purifying mg silicon in a simplified manner.

  In general, two approaches for the purification of silicon are well known: the chemical path and the metallurgical path. In the case of chemical purification, m.g. silicon is transferred to the gas phase in the form of chlorosilane and then deposited in the form of a chemical vapor deposition (CVD) process (e.g., the use of trichlorosilane such as the conventional Siemens method ( See, e.g., U.S. Pat. Nos. 2,999,735; 3,011,877; 3,979,490; and 6,221,155) or the use of silanes (see, e.g., 4,444,811 and 4,676,967)). In this case, the first step is the formation of chlorosilanes from small size (granulated / milled) silicon particles in a fluid bed reactor and the resulting distillation of gaseous species. Since silicon is used in the form of small particles that are completely exposed to the process gas, impurities (metal impurities, boron, phosphorus, etc.) can also be in the gas phase, and therefore for silicon deposition or silane Before chlorosilanes can be used for other chemical treatments such as hydrogenation for the production of these, they must be removed by distillation.

  The metallurgical approach is either simply as silicon (and removal of impurities by separation and oxidation, as disclosed for example in WO / 2008 / 031,229 A1) or an alloy of mg and silicon (eg aluminum) Requires the casting of mg silicon as In the latter case, the metal acts as a catcher / getter for impurities, but before the purified silicon is cast into an ingot, it must be wet-chemically leached. The metallurgical approach can also result in significantly lower purity levels than the chemical path.

  The main drawback of the chemical path is that during chlorosilane production, in fact, a stock of small sized particles of mg silicon is required to provide a large silicon surface for the reaction. . Furthermore, undesirably high pressures and / or high temperatures are required to keep the reaction between mg silicon and the process gas (HCl, or HCl, H2 mixture) proceeding. This can lead to high impurity (metal chloride, BCl3, PCl3, CH4, etc.) concentrations in the chlorosilane stream, which can require thorough purification by distillation.

  Metals such as copper are known to act as catalysts for the reaction between silicon and HCl because they lower the required temperature and increase the yield (eg, US Pat. No. 2009/0060818 A1). ). When used as a catalyst, copper (or rather copper in the form of copper chloride) is contacted with mg silicon particles, thereby increasing their reactivity with HCl. For this application, metals such as copper are only used as catalysts for separate mg silicon stock, so the concentration of applied metal / copper catalyst should be in the lower percent or permill range. is there. In this range, metals such as copper have no function for the purification or gettering (ie filtration) of impurities from mg silicon stock.

  The use of a copper-silicon alloy for the purification of mg silicon is described by Jerry Olson (US Pat. No. 4.481.232; RC Powell, JM Olson, J. of Crystal Growth 70 (1984) 218; P. Tejedor, JM Olson, J. of Crystal Growth 94 (1989) 579; see also P. Tejedor, JM Olson, J. of Crystal Growth 89 (1988) 220). Olson cast a copper-silicon piece larger than 20 wt% Si (eg, 20-30 wt%), which he placed in close proximity to the heated silicon filament. The entrained process gas (HCl-H2 mixture) extracted silicon from the alloy in the form of chlorosilane, and Olson was able to deposit purified silicon on the silicon filament. Silicon extraction was performed in the temperature range of 400-750 ° C. When using a metal silicon alloy, the presence of crystallites in the alloy material 16 (eg, when there are two phases in the alloy material), such as instability of the alloy material both inside and outside the refining process, etc. It should be appreciated that significant operational deficiencies can be encountered.

SUMMARY OF THE INVENTION The object of the present invention is to produce a vapor deposition transport gas from a low purity silicon source to prevent and / or mitigate at least one of the disadvantages indicated above, said low It is to provide a system, method and / or material for the purification of pure silicon and / or the production of the resulting high purity silicon.

  The present invention is a method for producing high-purity silicon, comprising a first chamber (chlorination chamber) configured to contain a gas source capable of carrying a silicon-metal alloy and silicon, and a first chamber A second chamber (deposition chamber) in which a second gas mixture is formed by the deposition of silicon, wherein the at least one filament is configured to receive silicon by deposition. A method of using the apparatus is provided. The first gas flow path is configured to pass a gas carrying silicon from the chlorination chamber to the deposition chamber, and the second gas flow path passes a second gas mixture from the deposition chamber to the chlorination chamber. It is configured as follows. The second gas mixture can serve as a gas source for chlorination of silicon when contained in the chlorination chamber.

  In another aspect, the present invention is a method of producing high purity silicon using an apparatus having a fluidly connected chlorination chamber and a deposition chamber, comprising: (i) providing a source of silicon in the chlorination chamber. Providing a suitable silicon-metal alloy; (ii) providing an initial first gas mixture comprising a source of hydrogen and chlorine; and (iii) in a chlorination chamber, the silicon-metal alloy; Actively heating the silicon-metal alloy to a temperature at which the first gas mixture reacts to form a silicon source gas containing at least one of one or more chlorosilanes; and (iv) Providing at least one filament in the deposition chamber configured to receive silicon therein; (v) the silicon source gas Heating said at least one filament to a temperature at which silicon is deposited on the surface of said at least one filament and producing a second gas mixture comprising a source of chlorine; (vi) a second gas mixture; There is provided a method comprising returning to a chlorination chamber to act as a gas mixture that reacts with the silicon alloy and (vii) repeating steps iii) and vi) until sufficient silicon is deposited.

  In a further embodiment, the present invention is a method of producing high purity silicon using an apparatus having a fluidly connected chlorination chamber and a deposition chamber, comprising: (i) providing a source of silicon in the chlorination chamber. Providing a suitable silicon-metal alloy; (ii) providing an initial first gas mixture comprising a mixture of H2, HCl and chlorosilane, which can provide a chemical vapor carrier gas for carrying silicon; (Iii) actively reacting the silicon-metal alloy in a chlorination chamber to a temperature sufficient to cause the initial gas source to react with the silicon-metal alloy to produce a process gas containing a gaseous silicon source. And (iv) depositing at least one filament configured to receive silicon therein; And (v) producing a second process gas source capable of depositing the gaseous silicon on the surface of the at least one filament and providing a chemical vapor carrier gas for carrying the silicon. Heating the at least one filament to a temperature; (vi) returning a second process gas source to the chlorination chamber to serve as a gas source that reacts with the silicon alloy; and (vii) repeating steps iii) and vi) until sufficient silicon is deposited on the at least one filament.

  Complex and expensive purification steps may be required in today's high purity silicon purification processes. Another drawback of today's process is the high impurity concentration in the chemical vapor, which may require thorough purification by distillation. Although hypereutectic alloys have been in the prior art process, there have been significant operational disadvantages such as instability of the alloy material both inside and outside the refining process. In contrast to this purification system and method, a method for purifying silicon comprising: reacting an injection gas with a metal silicon alloy material having a silicon weight percent less than or equal to the silicon eutectic weight percent defined for each metal silicon alloy Generating a chemical vapor carrier gas comprising silicon obtained from an atomic matrix of the metal silicon alloy material; flowing the vapor carrier gas through a filament configured to promote silicon deposition; Depositing silicon on the filaments from the chemical vapor carrier gas in a configured form.

  A further aspect provided is a method for purifying silicon, comprising reacting an implantation gas with a metal silicon alloy material having a silicon weight percent less than or equal to the silicon eutectic weight percent defined for each metal silicon alloy. Generating a chemical vapor carrier gas comprising silicon obtained from an atomic matrix of the metal silicon alloy material; flowing the vapor carrier gas through a filament configured to promote silicon deposition; Depositing silicon in purified form on the filament from a carrier gas.

  A further aspect is a metal silicon alloy material having a silicon weight percent that is at a selected eutectic weight percent of silicon defined for each metal silicon alloy for use in a chemical vapor deposition (CVP) process. , A material in which the presence of silicon crystallites in the alloy material is below a defined maximum crystallite threshold.

  A further aspect is a metal silicon alloy material having a silicon weight percent that is less than or equal to the silicon eutectic weight percent defined for each metal silicon alloy for use in a chemical vapor deposition (CVP) process.

  A further aspect is an apparatus for purifying silicon comprising: reacting an injected gas with a metal silicon alloy material having a silicon weight percent less than or equal to the eutectic weight percent of silicon defined for each metal silicon alloy, and said metal silicon A first reactor for generating a chemical vapor carrier gas comprising silicon derived from an atomic matrix of alloy material; an outlet for flowing the vapor carrier gas through a filament configured to promote silicon deposition; And a second reactor for depositing silicon from a chemical vapor carrier gas onto the filaments in a purified form.

  A further aspect is a metal silicon alloy material having a silicon weight percent that is at a selected eutectic weight percent of silicon defined for each metal silicon alloy for use in a chemical vapor deposition (CVP) process. , A material in which the presence of silicon crystallites in the alloy material is below a defined maximum crystallite threshold.

  A further aspect is a metal silicon alloy material having a silicon weight percent that is less than or equal to the silicon eutectic weight percent defined for each metal silicon alloy for use in a chemical vapor deposition (CVP) process.

  One objective is to use copper-silicon compounds to take advantage of the catalytic properties of copper and to control / getter impurities using a metal-silicon matrix.

  For example, low purity grade m.p. so as to produce high purity silicon for use as a raw material for photovoltaic applications. g. Another purpose is to purify the silicon.

  Further examples of purposes are: the production of copper-silicon sources for use in chlorination reactors, which (1) suppresses the formation of microcracks during casting and (2) has a desired shelf life. Suppresses significant oxidation, (3) suppresses swelling / expansion during use in the chlorination reactor, (4) suppresses dust or powder emissions during use in the chlorination reactor, (5) production of high purity silicon that exceeds a selected resistivity threshold and / or (6) production that can be controlled and remelted / cast (ie recycled) if the silicon becomes significantly poor It is.

  The present invention will now be described in more detail with reference to the following drawings.

FIG. 1 is a schematic cross-sectional view showing an apparatus according to the present invention for the production of chlorosilane and the deposition of high purity silicon in a closed loop configuration, wherein the two chambers are completely independent and connected by a piping system. Yes. FIG. 2 is a schematic cross-sectional view showing an apparatus according to the present invention for the production of chlorosilane and the deposition of high purity silicon in a closed loop configuration, in which two chambers are mounted but separated by an intermediate plate ing. FIG. 3 is a block diagram illustrating a typical refining process and apparatus using an alloy material as an example of the apparatus and method of FIG. FIG. 4 is an example of a phase diagram for the alloy material of FIG. FIG. 5 is an example of a matrix of the alloy material of FIG. FIG. 6 is an alternative embodiment of the eutectic nature of the metal alloy material for the apparatus of FIG. FIG. 7a shows the hypereutectic nature of the alloy material that is not desired in the apparatus of FIG. FIG. 7b shows the result of an example of the alloy material of FIG. 8a after use in the apparatus of FIG. FIG. 8 shows the oxidation behavior of the copper-silicon eutectic alloy material relative to the oxidation behavior of the hypereutectic alloy of FIG. 7a. FIG. 9a is a further embodiment of the alloy material of FIG. FIG. 9b shows the silicon content after being degraded in the steam generation process of the apparatus of FIG. FIG. 10 is a block diagram for an example method of the chemical vapor production and deposition process of FIG. FIG. 11 is a block diagram of an example of the chemical vapor production process of FIG. FIG. 12 is an example of a casting apparatus for the alloy material of FIG. FIG. 13 is a block diagram for an example of a casting process using the apparatus of FIG. FIG. 14a is a resistivity diagram measured through the thickness of deposited silicon obtained from the eutectic or hypoeutectic alloy material used in the apparatus of FIG. FIG. 14b is a resistivity diagram measured through the thickness of deposited silicon obtained from the eutectic or hypoeutectic alloy material used in the apparatus of FIG.

Detailed Description of the Preferred Embodiment
It has been recognized that a significant disadvantage of the copper-silicon alloy proposed by Olson is that the alloy appears to be hypereutectic, and applicants have found that the hypereutectic tends to oxidize when exposed to the atmosphere. It has been shown and confirmed that it swells and collapses during the chlorination process. The latter can be caused by the presence of a significant amount of silicon crystallites and associated cracks interspersed in the copper-silicon eutectic matrix in the alloy material.

  In the following description, many terms are used extensively, but the following definitions are provided to facilitate an understanding of the various aspects of the present invention. The use of examples in the specification, for example terminology, is for illustrative purposes only and is not intended to limit the scope and meaning of embodiments of the invention herein. Numeric ranges are inclusive of the numbers defining the range. In the specification, the term “comprising” is used as a non-limiting term and is substantially equivalent to the phrase “including, but not limited to”. The term “comprise” has a corresponding meaning. Furthermore, it will be appreciated that certain approaches, such as illustrated by example, can generally be aimed at controlling pressure, temperature, and / or percent silicon content in the alloy material 16. Minor changes in the specific means specified are acceptable if the effect of such differences is insignificant for the crystallite 120 content of processes 9, 11 and / or alloy material 16. For example, an approximate temperature can mean a temperature variation of several degrees above and below. For example, an approximate silicon weight percent can mean up and down within a range of 0.01-0.2 of a particular weight percent measurement.

  The present invention enables the purification of silicon, the production of chlorosilanes, and the deposition of high purity silicon in a recirculating closed loop system. At the beginning of the process, the chamber is filled with a mixture of H2 and HCl. The ratio of the two gases is in the range of 1: 9 to 9: 1 and preferably in the range of 1: 2 to 2: 1. Next, process gas is circulated between the chambers to produce chlorosilane in one chamber (referred to herein as a chlorination chamber) in which low purity silicon is installed in the form of a silicon-metal alloy, and a heated silicon filament is installed. On the other hand (referred to herein as the deposition chamber), silicon is deposited. When the rod is recovered and the silicon metal alloy is recharged through the chlorination chamber, a gas having a volume equivalent to the volume of the apparatus is removed and processed. It may be collected and stored in a separate tank for direct reuse, or further processed and neutralized as exhaust gas. The use of the term chlorosilane herein refers to any silane species having one or more chlorine atoms bonded to silicon. The chlorosilanes produced can include, but are not limited to, dichlorosilane (DCS), trichlorosilane (TCS), and silicon tetrachloride (STC). Preferentially, TCS is used for the deposition of purified silicon.

  The present invention provides an apparatus and method that facilitates the removal of metal impurities from a deposition process. In particular, the present invention provides a deposition method that uses silicon-metal alloys and provides removal of metal impurities in high purity silicon. Some metal impurities do not form volatile chlorides, such as Fe, Ca, Na, Ni or Cr, so they remain in the alloy material 12 in the chlorination chamber. Others that form chlorides with somewhat lower boiling points (eg, Al or Ti) evaporate, but more preferably condense in the deposition region 14 on a colder surface than deposits on the hot silicon filament 26. .

  As mentioned above, the chamber in which the purification process takes place is also referred to herein as a chlorination chamber. This chlorination chamber is that described in Applicant's co-pending application entitled Apparatus for the Production of Chlorosilanes. The chamber in which the deposition takes place is also referred to herein as the deposition chamber.

  In a further aspect, the present invention is a method for high purity silicon deposition, comprising a chlorination chamber configured to continuously produce a process gas source of chlorosilane, and a subsequent silicon deposition. And a deposition chamber configured to contain a process gas source.

  In a further aspect of the invention, two or more chlorination chambers are connected to one deposition chamber.

  In a further aspect of the invention, two or more deposition chambers are connected to one chlorination chamber.

  The chlorination chamber and the deposition chamber may be attached but separated by a diverter or plate, or they may be disconnected and connected by a piping system.

  In one embodiment, the chlorination chamber and the deposition chamber of the apparatus can accommodate an initial source of H2 and HC1, and once the apparatus has accommodated it, further addition of an external gas mixture other than the initial gas source Without, it is comprised so that chlorosilane gas may be produced | generated continuously.

  In another embodiment, the chlorination chamber contains a gaseous source of chlorine from within the closed loop apparatus (i.e., exhaust gases from the deposition process (a mixture consisting primarily of H2, HCl, TCS and STC)). This gas mixture can be used to make a larger amount of silicon into the gas phase in the form of chlorosilane. The present invention provides the ability to reconvert any excess STC that occurs during silicon deposition into a TCS.

  Any metal can be used to form the silicon-metal alloy used in the apparatus and method of the present invention, provided that the metal has a low vapor pressure and is limited to HCl gas and hydrogen. It should be reactive and the metal should not form gaseous species that tend to decompose on hot filaments in the deposition chamber. Preferably, the metal used does not form volatile metal chlorides over the operating temperature range of the chlorination chamber. Possible metals that form the alloy include, but are not limited to, copper, nickel, iron, silver, platinum, palladium, chromium, or combinations of these metals. In a preferred embodiment of the present invention, the alloy is a silicon-copper alloy.

  Silicon-metal alloys should contain at least 10% silicon to provide high productivity, but lower concentrations of silicon with lower productivity will work as well. In order to provide high productivity and improve selectivity, at least one component of the silicon-metal alloy should catalyze the hydro-chlorination of silicon.

  In a preferred embodiment, the material used for the chlorination process is formed from eutectic or hypoeutectic copper-silicon. Eutectic and hypoeutectic copper-silicon are notable for their low affinity for oxidation when exposed to the atmosphere. Furthermore, swelling or pulverization during the chlorination process is reduced. This reduces the risk of particle contamination in the gas stream. Furthermore, the process gas does not penetrate into the bulk of the material (in the case of a hypereutectic copper-silicon alloy, which occurs due to severe swelling of the hypereutectic material), thus improving impurity gettering. Therefore, reaction with the process gas can occur on the surface of the brick and fast diffusion of the elements will reach the surface. Silicon is known to have an unusually / preferentially high diffusion coefficient in copper-silicon (over that of the impurities in this alloy) and provide an excellent filter / gettering effect on impurities. ing.

  The alloy used can be any form that allows easy loading of the chamber and preferably provides a large surface to volume ratio, such as bricks, plates, granules, large chunks, pebble or any other shape Can take. This alloy may be produced by a casting process or may be sintered.

  The present invention relates to the production of high purity, cost effective silicon. Furthermore, the present invention relates to the purification of unpurified silicon, such as, but not limited to, metal grade silicon of about 98 to 99.5% purity to high purity silicon having a purity better than 6N with respect to metal impurities. . The present invention further provides a process and apparatus for the purification and production of solar grade silicon that can be used as a base material for forming, for example, polycrystalline or single crystal ingots for wafer manufacture.

  The present invention further provides an apparatus and method that allows direct control of the temperature of the silicon source, ie, the alloy, independent of the control of the filament on which the silicon is deposited.

  The chlorination chamber of the present invention is dimensioned to contain the alloy and contain the initial process gas described herein. There is no size limitation for the chlorination chamber, except for structural and mechanical reasons. It will be appreciated that the chlorination chamber should be connected to or include a heating system configured to heat the chlorination chamber as described herein. The chamber may be cylindrical, box-shaped, or any geometric shape suitable for the process described. In one embodiment, the chamber is cylindrical that provides easier evacuation and better overpressure properties. The chamber is configured to be heated by an internal heater or by an external heater connected to the chamber, as described in more detail below.

  The chamber can be manufactured from any material that can withstand a corrosive atmosphere and a range of operating temperatures. In order to hold the silicon-alloy in place, a charge carrier may be used, which must withstand the same atmosphere and temperature as the chamber and is therefore made from a similar material. However, it does not form an alloy within the temperature used for the process.

  The chamber includes an inlet and an outlet for process gas. Preferably, the inlet and outlet are designed to provide a uniform flow of process gas to the alloy enclosed in the chamber. A flow guide system may be used to improve uniformity. The outlet may comprise a mesh or particle filter depending on the application in which the gas exiting the chamber is used.

  The chamber may further include an agitator to provide additional circulation within the chamber and to assist in the transfer of process gas. In one embodiment, the chamber may include an agitator that is an internal propeller. This propeller may be incorporated anywhere in the chamber provided that uniform movement of the gas is provided. Alternatively, the chamber may be connected to an external pump, such as a pump or blower that assists in the transfer of process gas within the chamber. The pump or blower should be made of a material that is exposed to corrosive gases and can therefore withstand such conditions. An external pump may be installed near the inlet or outlet.

  The silicon-metal alloy placed in the chamber is actively heated to an appropriate temperature to ensure a fast reaction between the process gas and silicon and to ensure high power. As explained above, the chamber may include a heating device or may be connected to an external heating device. The heating device is used to heat the chamber and the alloy directly, i.e. it is the main heat source. The term “aggressive heating”, or variations thereof, is used to describe a controlled method of heating an alloy wherein the temperature of the alloy is altered by changing the output of the heating device. The temperature of the exhaust gas entering the chlorination chamber from the deposition chamber provides an additional heat source in addition to the exothermic reaction of chlorosilane formation, which is an indirect order. Control of the alloy temperature is directly related to the heating device.

  For internal heating devices, graphite heaters, preferably SiC coated, or any other material suitable for use in a corrosive atmosphere can be used. The internal heating device provides enhanced heating for large diameter reactors and further allows the chamber to operate at lower wall temperatures to improve the corrosion resistance of the vessel material. If an external heating device is used, any type of resistance heater may be used and connected to the chamber. The external heating device can be placed near the outer wall of the chlorination chamber, which can be connected directly to it or can be part of the chamber wall. From the description presented here, it will be appreciated that excellent thermal contact between the heating device and the chamber is required while providing a uniform temperature distribution within the chamber. It will further be appreciated that the number of heating devices and their location are designed so that the heating of the alloy occurs as efficiently and uniformly as possible. By using process gas preheating on the gas inlet side, uniform heating of the alloy can be improved. In addition to the heating device, the apparatus may further include a thermal insulation to reduce heat loss from the chamber, which may be placed around the chamber, thereby enclosing the heating element and the chamber. . Since this insulation material is not exposed to the process gas at any time, any insulation material in the state of the art can be used.

  The temperature can be controlled by a state-of-the-art temperature controller. The temperature of the silicon alloy should be higher than 150 ° C., preferably higher than 300 ° C. and not higher than 1100 ° C. in order to achieve a high production rate. Those skilled in the art will know that when using a gas mixture of hydrogen and HCl as the injection gas, too high a temperature will shift the equilibrium reaction between silicon and hydrogen chloride gas to one side and the chlorosilane on the other side towards solid silicon. Will admit that it will shift. When using pure copper-silicon alloy, the temperature should not exceed 800 ° C. This is because it indicates the eutectic temperature of the copper-silicon alloy. More preferably, the temperature should be kept within the range of 300 to 500 ° C. in order to optimize the formation of trichlorosilane. If a higher melting point metal-silicide is used as the feed, it will be higher. The chamber temperature can be controlled and / or monitored by a thermocouple or any other type of temperature sensor. It will be appreciated that although the temperature sensor is preferably attached to the alloy, this need not be the case and those skilled in the art will be able to control the alloy temperature based on the power consumption of the heating element.

  The pressure in the reactor is controlled higher than atmospheric pressure. In one embodiment, the pressure is in the range of 1-10 bar. In another embodiment it is about 5 bar.

  In one embodiment, the alloy is placed in a chamber so that the surface of the alloy is fully exposed to the gas stream. The alloy is preferably copper and low purity silicon, such as metal grade silicon. However, it will be understood that higher purity silicon may be used. The silicon concentration should be at least 10 at% to ensure high silicon productivity. However, lower silicon concentrations can be used as well, generally without compromising the process. In a preferred embodiment, the material used for the chlorination process is formed from eutectic or hypoeutectic copper-silicon. Eutectic and hypoeutectic copper-silicon are notorious for their low affinity for oxidation when exposed to the atmosphere. Furthermore, it may not swell or powder during the chlorination process. This can reduce the risk of particle contamination in the gas stream. Furthermore, the process gas does not penetrate into the bulk of the material (in the case of a hypereutectic copper-silicon alloy, which occurs due to severe swelling of the hypereutectic material), thus improving impurity gettering. During the alloy casting process, additional additives may be added to speed up the reaction time during chlorosilane formation. Other additives that can be used include, but are not limited to, chromium (Cr), nickel (Ni), iron (Fe), silver (Ag), platinum (Pt), and palladium (Pd).

  The silicon-metal alloy may be placed in the chlorination chamber in the form of a fixed bed arrangement or in the form of a moving bed or any other type of stirred bed arrangement. Recharging of the silicon-metal alloy during this process can be provided using an additional inlet in the chlorination chamber.

  The initial process gas used is a gas that can react to form a chemical vapor carrier gas suitable for carrying silicon. In one embodiment, the initial process gas provides a source of chlorine. In one embodiment, the initial process gas is hydrogen and dry HCl gas supplied to the chamber through the inlet and the alloy is a copper-silicide alloy. The ratio of hydrogen and dry HCl gas is in the range of 1: 9 to 9: 1, preferably in the range of 1: 5 to 5: 1, or more preferably in the range of 1: 2 to 2: 1. In this embodiment, the gas mixture exiting from the chlorination apparatus can be supplied directly to the silicon deposition chamber.

  Prior to the start of the process, the system is purged with a dry, oxide-free gas or evacuated to provide an oxide-free atmosphere for the process.

Once supplied, the initial process gas reacts with silicon at the surface of the silicon-metal alloy. As a result, chlorosilanes such as trichlorosilane (TCS), silicon tetrachloride (STC) or dichlorosilane (DCS) are produced by the reaction of the H2-HCl mixture with a silicon alloy. This reaction provides a chemical vapor carrier gas for carrying silicon. To simplify, this reaction can be written as:
Si + 3HCl → SiHCl3 + H2

  Typical byproducts of this reaction are SiH2Cl2 (DCS) and SiCl4 (STC).

  The selectivity of the reaction shifts towards TCS for low temperature silicon-metal alloys and towards STC at higher alloy temperatures.

  Chlorosilane is actively carried from the chlorination chamber to the deposition chamber. The deposition rate of silicon can be controlled by the flow rate (ie, gas exchange rate) between the chlorination chamber and the deposition chamber. This flow rate may be controlled by a control system connected to the apparatus and configured to control the flow of gas in and to the chlorination chamber and the deposition chamber. Alternatively, it can be controlled by H2 vs. HCl or it can be controlled by the temperature of the filament. The deposition rate will also depend on the amount of silicon-metal alloy placed in the chlorination region 12.

As stated above, gaseous silicon is then deposited as high purity silicon on a heated filament in a deposition chamber. The types of filaments that can be used include, but are not limited to, silicon, graphite, molybdenum, tungsten, or tantalum filaments. The filaments can be of any shape that allows subsequent deposition of silicon 27 thereon. Preferably, the filament is U-shaped. The temperature of the filament is controlled and maintained within the range of 1000 to 1200 ° C. To simplify, the decomposition looks like this:
SiHCl3 + H2 → Si + 3HCl

  Typical byproducts of this reaction are SiH2Cl2 (DCS) and SiCl4 (STC).

  For a more detailed discussion of various chemical reactions and reaction steps, see, for example, A. Luque and S. Hegedus (Eds.): “Handbook of Photovoltaic Science and Engineering”, Wiley & Sons Ltd, ISBN 0-471-49196- It is shown in 9. The post-reaction gases shown above are pumped back into the chlorination chamber where they are again used for the formation of chlorosilanes. In this way, a closure that (a) minimizes the amount of process gas produced, (b) lowers the costs associated with the infrastructure for storage and transport of chlorosilanes, and (c) reduces the effort for exhaust gas treatment. The system is established.

  Since the process gas circulates at a conveying speed several times greater than the volume of the system per hour, only one part of the chlorosilane (mainly TCS) reacts on the filament in one cycle and the rest is chlorinated. Return to the chamber.

  In one embodiment, the deposition chamber is a Siemens reactor with a bell jar. Gas inlets and outlets and electrical feedthroughs are incorporated into the bottom plate. It will be appreciated that the chamber walls should be cooled to avoid heating the walls.

  In another embodiment, the gas inlet and outlet are located at the bottom and top of the chamber, respectively. This arrangement provides a directional flow of process gas.

  In another embodiment, the deposition chamber is connected to a chlorination chamber and the two chambers are separated but placed close to each other. In this embodiment, some of the heat dissipated from the filament is used to support aggressive heating of the silicon-metal alloy, improving the energy balance of the system.

  It will further be appreciated that the chemical vapor carrier gas composition produced from the reaction in the chlorination chamber is then fed directly into the deposition chamber. An intermediate step for the filtration / treatment of the chemical vapor carrier gas may be between the chlorination chamber and the deposition chamber, but at least a portion of the chemical vapor carrier gas composition produced by the chlorination chamber may be (E.g., contaminants may be filtered, but the chemical vapor carrier gas chlorosilane composition desired for deposition purposes is still contained in the deposition chamber).

  The present invention is capable of adjusting the filament temperature to a temperature in the range of 1000 ° C. to 1200 ° C., provided that an appropriate flow rate of gas is provided to achieve deposition at the required amount and purity level. It is not limited to a specific chamber geometry. There is no limit on the number of rods incorporated into the deposition chamber, except for structural and design reasons.

  In addition to impurity gettering with copper silicide, the apparatus includes one or more additional components, such as condensers (so-called “salts and wraps”) or deposited silicon to capture volatile impurities such as metal chlorides, for example. A particle filter that further reduces the concentration of impurities therein may be further included.

  The salt trap is characterized by a region with a low flow rate and a large and cooled surface, favoring the condensation of volatile metal chlorides having a boiling point higher than that of chlorosilane used for silicon transport. . The temperature inside the salt trap should not be less than about 60 ° C. to avoid condensation of silicon tetrachloride. The salt trap can be incorporated directly into the gas loop, or it can be installed in the bypass loop so that only a portion of the gas stream is directed through the salt trap at a time.

  As the particle filter, any dust collector having a technical level can be used as long as it is suitable for a corrosive atmosphere. Again, this filter may be incorporated directly into the gas loop or installed in the bypass loop.

  In an alternative embodiment, the apparatus of the present invention further allows for pre-treatment or etching of the silicon-metal alloy in the chlorination chamber prior to entering the process gas into the chamber. In this embodiment, the deposition chamber is shut off with respect to the chlorination chamber, i.e. no gas in the chlorination chamber can flow to the deposition chamber, and a suitable etching gas mixture is supplied to the deposition chamber. Is done. Examples of the types of gas mixtures that can be used include H2 and HCl.

  The present invention will now be discussed in more detail with reference to the accompanying drawings. In the illustrated embodiment, copper-silicide is provided as the initial source of silicon.

  FIG. 1 shows a schematic cross-sectional view of an apparatus, generally designated 10, used for the production of chlorosilane from a silicon-metal alloy and the production of purified silicon by a chemical vapor deposition (CVD) process. Chlorination is performed in the first container or chamber 12 and high purity silicon deposition is performed in the second container or chamber. The containers 12, 14 are manufactured from a material that is not damaged by and resistant to the process gas. The alloy 16 is placed in the first container 12 so that the maximum surface area is directed to the gas flow. An initial gas mixture, such as H2 and HCl, is fed into the chamber via an inlet 18 and at the end of the process, the process gas is pumped through an outlet 20 installed in the second vessel 14. . Valves 22a, 22b close the loop during this process.

  The use of valve 22a or 22b further allows for the sampling of process gases during the process for process gas analysis or the addition of special gas species or the change of the H2 to HCl ratio.

  When the initial gas flow enters the container 12, the valve 22a is closed to ensure a closed loop system. It will be appreciated that the valve 22b will be closed before the initial gas flow is supplied to the vessel 12. The heating device 38 is then used to actively apply heat to the alloy 16 and when the temperature of the alloy exceeds 150 ° C., the initial gas mixture reacts with the surface of the alloy 16 to form a gaseous silicon. A source, chlorosilane, is produced. The chlorosilane gas then leaves the container 12 via the outlet 24 and flows to the container 14.

  In the container 14, at least one U-shaped filament 26 is installed, on which silicon is deposited. Filament 26 is heated to a temperature in the range of 1000 ° C. to 1200 ° C. to allow silicon deposition. The resulting gas containing mainly H2, HCl, TCS and STC then exits the container 14 and returns to the container 12 through the second flow path. This gas then acts as an initial chlorine source so that no additional gas source is needed other than what occurs in the closed loop system. The STC, or part thereof, will convert back to TCS, and the HCl, or part thereof, will react with low purity silicon from a silicon-metal alloy to chlorosilane, primarily TCS. The gas is actively circulated everywhere by the pump 30, and the conveyance speed is measured by the flow meter 32. In the salt trap 34 at the outlet of the chlorination chamber, volatile impurities are condensed and captured. Particles can be captured by the particle filter 36.

  Since particles and metal chloride originate primarily from the chlorination chamber, a more preferred location for the particle filter and salt trap is after the chlorination chamber outlet. However, it will be understood that these members are not essential and that the apparatus and method described herein will function without these members.

  In addition, any state-of-the-art blower or delivery pump can be installed between the two chambers, provided that it can handle corrosive gases.

  The installation of the inlet 28 and outlet 24 is shown as entering the container 12 from the top for the inlet and exiting the container 12 for the outlet 24 from the outlet. However, the arrangement of the inlet and outlet may be different from that shown.

  In FIG. 2, the deposition chamber 13 is attached to the chlorination chamber 12 so that the hot gas exiting the deposition chamber is used to serve as an additional heat source for the silicon alloy. Such an arrangement improves the energy efficiency of the system. Depending on the amount of alloy used or the amount of silicon deposited, the size and volume of the two chambers can vary.

  In either case, i.e. in a completely disconnected or attached arrangement, a guide system for the process gas can be incorporated in one or more chambers to optimize the gas flow in the corresponding chamber. Good but not shown.

An analysis of the purity of the deposited silicon formed by the method described herein and the metal grade silicon used to form the alloy is shown in Table 1. A representative sample is shown. All other elements not shown were below the detection limit. Silicon was analyzed by GDMS (glow discharge mass spectrometry, copper detection limit is 50 ppb) by an independent accredited laboratory (NAL-Northern Analytical Lab., Londonderry, NH).

  The following examples are provided to further illustrate the performance of the method and apparatus of the present invention. These are merely examples and are not limiting in any way.

Example 1
A chlorination chamber with a diameter of 34 cm and a height of 50 cm is charged with 25 bricks of silicon-copper alloy, the total weight of the alloy is 12 kg and the silicon concentration is 30 wt%, ie 3.6 kg. Met. These bricks were installed at equal intervals in the center of the chlorination chamber. After proper evacuation and filling the chamber with process gas, the chlorination chamber was connected to a Siemens polysilicon deposition chamber. The pressure in this chamber was maintained above atmospheric pressure. The alloy was heated to a temperature of 300-400 ° C. and process gas was circulated in a closed loop system between the chlorination chamber and the deposition chamber. Chlorosilane (mainly trichlorosilane) generated in the chlorination chamber is consumed in the deposition chamber and exhaust gases from the deposition process (especially enriched by HCl and STC) are renewed by reacting with the silicon alloy. Used to produce fresh chlorosilane. The gas circulated for 48 hours, during which time 1.6 kg of silicon was extracted from the silicon-copper alloy and deposited in the deposition reactor. Copper is not detected in the deposited silicon and silicon is analyzed by GDMS (glow discharge mass spectrometry, copper detection limit is 50 ppb) and by an independent accredited laboratory (NAL-Northern Analytical Lab., Londonderry, NH) did. The resolution limit of copper is 50 ppb, which clearly shows that copper remains in the solid phase and only silicon is extracted from the alloy in the gas phase. The alloy brick inserted in the form of a solid piece formed a porous, somewhat sponge-like material that allowed for excellent gas exchange even when silicon had to be extracted from the area inside the alloy brick . After the process was stopped and the reactor was cooled, the gas was replaced with inert gas.

Example 2
A 4-piece silicon copper alloy (total weight: 1.3 kg, silicon amount: 390 g) was placed in a chlorination chamber with a diameter of 15 cm and a height of 25 cm. This alloy was heated by an external device and the process gas was circulated by an external membrane pump. Inside the deposition chamber, a filament was placed, heated to 1100 ° C., and the produced chlorosilane was consumed. The chlorination and deposition chamber is configured in a mounted arrangement and uses a portion of the filament heat to heat the silicon-copper alloy. The deposition chamber is separated from the chlorination chamber by an intermediate plate (made of quartz disk and copper plate). The central hole allows for excellent gas exchange. For alloy casting, metal grade silicon having a purity of 99.3% was used. According to GDMS measurements (average of two measurements from different areas of volume silicon), the total amount of metal impurities was less than 250 ppb (specifically: Al: 20 ppb, Mg: 5 ppb, Ca: 45 ppb, Fe: 21 ppb, Na: 56 ppb, K: 54 ppb, all other metals: below detection limit). The boron concentration was 0.22 ppm and the phosphorus concentration was below the detection limit (<10 ppb).

Example 3
A 10 kg mass having a size of about 1 ccm was placed in a chlorination chamber with a diameter of 34 cm and a height of 50 cm. This mass was formed from a copper-silicon alloy having a silicon concentration of 30 at%. Within 38 hours, 2 kg of purified silicon was deposited on two 34 cm high 10 × 10 mm filaments. The deposition temperature was 1100 ° C. The analysis results of impurities are shown in “Run 3.2-17” in Table 1.

Example 4
28 kg of eutectic copper-silicon (Si content 16 wt%) 16 was placed in the chlorination chamber 12 in the form of 88 bricks. The chamber 12 was connected to a silicon deposition reactor 14 to consume the produced chlorosilane and to provide the system with fresh HCl generated during the deposition process. Within 77 hours, 3.1 kg of silicon was extracted from the eutectic copper-silicon, transferred to gas form, and deposited on a heated silicon filament (filament temperature: 1050-1100 ° C.). The eutectic copper-silicon was heated to a temperature of 350-450 ° C. The initial gas composition supplied to the chlorination chamber was a mixture of H2 and HCl (60% H2 and 40% HCl). During this process, the chlorination chamber was fed only with off-gas from the deposition reactor. After this process, the integrity of the eutectic copper-silicon plate was obtained and no swelling or pulverization of the plate was observed. The purity of the deposited silicon was analyzed by GDMS: boron and phosphorus were below the detection limit of 10 ppb. As metal impurities, only Na, K, Al and F were detected, and all other elements were below the detection limit of GDMS. In total, the amount of detectable metal impurities was <100 ppb.

Example 5
54 kg of hypoeutectic (pure eta phase, Si content 12 wt%) copper-silicon 16 was placed in the chlorination chamber 12 in the form of 110 bricks. The temperature during the chlorination process was in the range of 270-450 ° C. The chamber 12 was connected to a silicon deposition reactor 14 to consume the produced chlorosilane and to provide the system with fresh HCl generated during the deposition process. Within 117 hours, 4 kg of silicon was extracted from hypoeutectic copper-silicon, transferred to gas form, and deposited as polysilicon on a heated silicon filament. The filament temperature was 1050-1100 ° C. The rod morphology was very smooth and no popcorn growth or morphological instability was observed. The initial gas composition supplied to the chlorination chamber was a mixture of H2 and HCl (60% H2 and 40% HCl). During this process, the chlorination chamber was fed only with off-gas from the deposition reactor. After this process, the integrity of the hypoeutectic copper-silicon brick was obtained and no swelling or pulverization of the plate was observed.

Example 6
1.4 kg of Ni—Si alloy having a nickel concentration of 60% was placed in the chlorination reactor 12 and heated to 350 to 450 ° C. Over a 27 hour period, 67 g of silicon was extracted from the nickel-silicon alloy and deposited on the heated silicon filament. During the process, the nickel-silicon alloy did not change its shape and did not show any signs of swelling, powdering or particle release.

Alternative Embodiment of Apparatus 10 and Associated Processes Referring to FIG. 3, this relates to a method 8 for manufacturing high purity silicon 27. In particular, this relates to a method 8 for producing high purity silicon 27 from low grade source material 16. This further provides a source 16 for the production of chlorosilane 15. In particular, this provides a method for producing chlorosilane 15 from eutectic or hypoeutectic silicon-metal alloy 16. This also relates to the production of high purity, cost effective silicon 27. The high-purity silicon 27 can be useful as a base material for forming, for example, a polycrystalline or single crystal ingot for wafer manufacture. Furthermore, it has a high purity with a selected resistivity above a resistivity threshold (eg, greater than about 50 ohm cm) of unpurified silicon, eg, metal grade silicon (about 98-99% purity). Further relates to purification to pure silicon.

Process 8 and device 10
In general, the melting point of a mixture of two or more kinds of solids (for example, metal silicon alloy material 16 (hereinafter also referred to as alloy material 16)) depends on the relative proportions of the component elements A and B. See FIG. 4 and FIG. In addition to the following, the alloy material 16 promotes the formation of chemical vapors, such as chlorosilane, from copper-silicon compounds or other silicon-metal alloys of a selected composition containing a selected degree of eutectic properties. select.

  Referring to FIG. 3, an alloy material 16 is provided that is used as a source for the production of a carrier gas 15 containing, for example, chlorosilane. The general desired properties of the alloy material 16 as well as the general process for the production of chlorosilane 9 (in the carrier gas 15) from the eutectic and / or hypoeutectic metal-silicon alloy material 12, as well as the alloy An example of the production of material 16, its use in one example of chlorosilane deposition process 8, and recycling will be described. It will be appreciated that the following description provides a metal / silicon alloy material 16 having desirable properties for use in, for example, a CVD process 8 performed in a CVD apparatus. The following example of the CVD process 8 and corresponding apparatus 10 is described as a chlorination 9-deposition 11 for discussion purposes only. It is contemplated that CVD processes 8 (including steam production 9 and deposition 11) and corresponding apparatus 10 other than those intended for chlorination can also be used with the alloy material 16 if desired. Chlorosilane is an example of a carrier gas 15 that is generated as a result of the reaction between silicon in the alloy material 16 and an injection gas 13 (eg, containing HCl). Other examples of the carrier gas 15 may include other halides (eg, reactive forms of fluorine, bromine and / or iodine with silicon, HBr, HI, HF, etc.). Thus, due to the different boiling points of the hydrogen halide and the different reactivity of the injection gas 13 with the silicon of the metal silicon alloy material 16, with respect to temperature, gas composition, pressure and / or other parameters associated with the processes 9, 11. Certain changes may be required. In addition, compatibility with certain materials used for or during process 9,11 must be provided.

  Examples of CVD include, but are not limited to: those classified by operating pressure; those classified by physical characteristics of vapor; plasma method; atomic layer CVD (ALCVD); hot wire CVD (HWCVD); Chemical hybrid vapor deposition (HPCVD); rapid thermal CVD (RTCVD); and vapor phase epitaxy (VPE). The operating pressure and / or temperature of the carrier gas generation process 9 is adapted to the melting point of the alloy material 16 (eg, the temperature of the process 9 is such that it is compatible with (ie, facilitates) the formation of the carrier gas 15. , Lower than the melting temperature of the alloy material 16), and / or to accommodate and / or otherwise facilitate the diffusion of silicon through the matrix 114 to diffuse any impurities contained in the alloy material 16. (E.g., greater than this-eg, at least 2 times greater, at least 4 times greater, at least an order of magnitude greater, at least 2 orders of magnitude greater).

  In general, chemical vapor deposition (CVD) is a chemical process 8 used to produce high purity, high performance solid materials such as deposited silicon 27 of the desired purity. Process 8 (eg, including the chlorination 9-deposition 11 process) can be used in the semiconductor and solar cell industries to produce silicon 27 of the desired purity and shape. In a typical CVD process 8, a silicon substrate 26 (eg, a filament such as a wafer or shaped rod) is obtained from one or more volatile precursors (ie, carrier gas 15 produced by chlorination process 9). The deposition process 11 of silicon 27 on the substrate 26 is accelerated. Thus, in the deposition process 11, the chlorosilane in the process gas 15 reacts on the substrate 26 and / or otherwise decomposes to produce the desired deposited silicon 27.

  Further, the process 8 can also be used for the production of high purity, cost effective silicon 27, for example provided as a component of unpurified silicon, such as, but not limited to, metal / silicon alloy material 16. About 98 to 99.5% pure metal grade silicon can be applied to the purification of high purity silicon 27 having a purity superior to a selected purity level (eg, 6N) with respect to metal impurities. Process 8 can also be used for the purification and manufacture of solar grade silicon 27, which can be used, for example, as a base material for forming polycrystalline or single crystal ingots for wafer manufacture.

  Referring again to FIG. 3, the injection gas 13 (eg, providing a chlorine source including hydrogen gas and dry HCl gas) is used to produce a chemical vapor (eg, chlorination) of the vapor deposition (eg, chlorination-deposition) apparatus 10. Pour into region 12 (eg, chamber) and contact with alloy material 16 (eg, copper-silicide alloy). The injection gas 13 reacts with the alloy material 16 to convert silicon from the alloy material 16 in the vapor production region 12 (eg, chamber, part of the chamber) to the deposition region 14 (eg, chamber, part of the chamber) of the apparatus 10. ) Is a gas capable of forming a chemical vapor carrier gas 15 for transporting to).

  Similar to the above example, process 8 and apparatus 10 provide for the purification of silicon by production of carrier gas 15 containing chlorosilane and the deposition of high purity silicon 27 on silicon filaments 26. The chlorosilane gas 15 is generated 9 in one region 12 where low purity silicon is installed in the form of a silicon alloy material 16, and the high purity silicon 27 is the other region where the heated silicon filament 26 is installed. Is deposited 11. The use of the term chlorosilane herein refers to any silane species having one or more chlorine atoms bonded to silicon. The chlorosilanes produced can include, but are not limited to, dichlorosilane (DCS), trichlorosilane (TCS), and silicon tetrachloride (STC). For example, TCS can be used for the deposition of purified silicon 27.

  Further, in process 8 described above, the use of alloy material 16 can facilitate the removal of metal impurities from deposition process 11. In particular, this deposition method can provide for the removal of metal impurities present in the alloy material 16 in the high purity silicon 27. Some metal impurities, such as Fe, Ca, Na, Ni or Cr, do not form volatile chlorides, so they remain in the alloy material 12 in the chlorination region 12. Others that form chlorides with somewhat lower boiling points (eg, Al or Ti) evaporate, but more preferably condense in the deposition region 14 on a colder surface than deposits on the hot silicon filament 26. .

Example of Parameters for CVD Process 8 Once the infused gas stream 13 enters the region 12, the heating device 6 is used to actively apply / supply heat 7 to the alloy material 16 so that the temperature of the alloy material 16 is a selected temperature T. When higher than (eg, 150 ° C.), the injected gas reacts at the surface of the alloy material 16 to produce a gaseous source of silicon, the chlorosilane carrier gas 15. The chlorosilane gas 15 then leaves this area and flows to area 14.

  At least one shaped (eg, U-shaped) filament 26 is placed in region 14 where silicon 27 is deposited. Filament 26 is heated to a temperature in the range of 1000 ° C. to 1200 ° C. to allow silicon deposition 11. A selected weight percent of silicon (eutectic silicon wt% composition or less) such that the presence (if any) of crystallites 120 (see FIG. 7a) in alloy material 16 is less than or equal to the selected maximum crystallite threshold. Silicon-metal for use in apparatus 10 and process 8 using silicon (in the case of eutectic or hypoeutectic matrix 114), the presence of crystallites 120 in alloy material 16 is negligible even if present. Any metal can be used to form the alloy material, provided that the metal has a vapor pressure below a defined vapor pressure threshold and exhibits limited reaction with HCl gas and hydrogen. . For copper silicon alloy material 16, the maximum crystallite threshold is, for example, less than 20%, less than 19%, less than 18%, less than 17.5%, less than 17%, or 16 as the weight percent of silicon in alloy material 16. It may be defined as less than 5%.

  Further, for example, the metal should not form gaseous species that tend to decompose on the hot filament 26 in the deposition region 14. Preferably, the metal used does not form volatile metal chlorides within the operating temperature range of the chlorination zone 12. Possible metals that form alloy material 16 include, but are not limited to, copper, nickel, iron, silver, platinum, palladium, chromium, or combinations of these metals. In a preferred embodiment of the present invention, the alloy material 16 is a silicon-copper alloy.

  As a result, chlorosilane gas 15 (eg, trichlorosilane (TCS), silicon tetrachloride (STC), or dichlorosilane (DCS)) is generated by reaction 9 between H 2 -HCl mixture 13 and silicon alloy material 16. This reaction 9 provides a chemical vapor carrier gas 15 for carrying silicon. To simplify, reaction 9 can be written as:

Si + 3HCl → SiHCl3 + H2
Typical byproducts of this reaction are SiH2Cl2 (DCS) and SiCl4 (STC).

  The chlorosilane gas 15 is actively carried from the chlorination region 12 to the deposition region 14. The deposition rate 11 of the silicon 27 can be controlled by the flow rate (ie gas exchange rate) between the chlorination and deposition regions 12,14. This flow rate may be controlled by a control system connected to the apparatus 10 and configured to control the flow of gases 13, 15 in and into the chlorination and deposition regions 12, 14. Alternatively, the flow rate can be controlled by the H 2 to HCl ratio or other ratio of the injected gas 13, or the flow rate can be controlled by the temperature of the filament 26. The deposition rate 11 may also depend on the amount of silicon-metal alloy material 16 placed in the chlorination region 12, the temperature T of the alloy material 16, and / or the wt% of silicon in the alloy material 16.

As described above, gaseous silicon in the carrier gas 15 is then deposited as high purity silicon 27 on the heating filament 26 in the deposition region 14. Types of filaments 26 that can be used include, but are not limited to, silicon, graphite, molybdenum, tungsten, or tantalum filaments. Filament 26 may be of any shape that allows subsequent deposition 11 of silicon 27 thereon. The temperature of the filament 26 is controlled and maintained within the range of 1000 to 1200 ° C. To simplify, the decomposition 11 can be as follows:
SiHCl3 + H2 → Si + 3HCl
Typical byproducts of this reaction 11 are SiH2Cl2 (DCS) and SiCl4 (STC).

  Furthermore, the silicon-metal alloy material 16 may be installed in the chlorination region 12 in the form of a fixed bed arrangement, or may be installed in a moving bed or any other type of stirred bed configuration. . Recharging of the silicon-metal alloy material 16 during process 9 may be performed using a recharging inlet in the chlorination area.

Structure of metal-silicon alloy material 12 Generally, the melting point of a mixture of two or more kinds of solids (for example, metal-silicon alloy material 16 (hereinafter referred to as alloy material 16)) depends on the relative proportions of the component elements A and B. To do. See FIG. 4 and FIG. In the alloy material 16, the main / major component element B is a metal (for example, copper Cu, nickel Ni, iron Fe, silver Ag, platinum Pt, palladium Pd, chromium Cr, and / or a combination thereof), and the smaller one It is recognized that the constituent element of is that containing silicon Si. Therefore, the metal silicon (Si) alloy material 16 is a metal / silicon alloy in which silicon occupies a volume (for example, 10-16%) of the alloy structure 114 that is smaller than the volume ratio of the metal (for example, Cu). Can be characterized as

  The eutectic material or the eutectic alloy material 16 is a mixture in which the melting point is in such a ratio that it is the minimum value of the local temperature T. This is because all the constituent elements A and B are from the solution of the molten liquid L at this temperature. It means to crystallize at the same time. Such simultaneous crystallization of the eutectic alloy material 16 is known as a eutectic reaction, the temperature T at which it occurs is the eutectic temperature T, and the composition and temperature of the alloy material 16 at which it occurs is eutectic. It is called point EP. With respect to the alloy material 16, this can be defined as a partial or complete solid solution of one or more elements A, B in the metal matrix / lattice 114 (see FIG. 5). Fully solid solution alloys give a single solid phase microscopic structure, while partial solutions give more than one phase, which depend on the thermal (heat treatment) history but can be homogeneous in distribution. It will be appreciated that the alloy material 16 has physical and / or chemical properties different from those of the component elements A, B. With respect to matrix / lattice 114, this can be defined as the structure (eg, crystalline or crystalline) of a clearly ordered component A, B of a solid material, where component A, B is an atom, molecule or ion As a regular repeating pattern extending in two and / or all three spatial dimensions.

  The eutectic or hypoeutectic metal-silicon alloy 16 is a silicon crystallite 120 that can be observed in the case of a hypereutectic alloy when the eutectic or hypoeutectic alloy 16 cools the cast alloy. It can be distinguished from a hypereutectic alloy in that it does not show the formation of. This lack of microcrystals 120 may provide an advantage when eutectic or hypoeutectic silicon-copper alloys are used, for example, as a source material for process 8 described herein.

  Referring to FIG. 4, there is shown an example of a phase equilibrium diagram for a binary system including a mixture of two kinds of solid elements A and B, where the eutectic point EP is the liquid phase L is the solid phase α + β. It is a point that is directly adjacent to. Thus, phase diagram 115 plots the relative weight concentrations of elements A and B along horizontal axis 117 and temperature T along vertical axis 118. The eutectic point EP is the point where the liquid phase L is immediately adjacent to the solid phase α + β (eg, a homogeneous mixture of both A and B) and is the minimum melting of any possible alloy of the component elements A and B. It represents temperature. The phase diagram 115 shown is found to be for a binary system (ie, components A, B), but uses other systems (eg, ternary systems A, B, C and higher). In combination with the metal (or a mixture of various metals) as the higher component element (or element group) B, Si is contained in the lower component A (for example, Si is one or more kinds). It is conceivable that the alloy material 16 can be defined such that the component element A is smaller than the main component / element group including various metals “B”. Examples of alloy material 16 include, but are not limited to: silicon-copper alloy; silicon-nickel alloy; silicon-iron alloy; silicon-silver alloy; silicon-platinum alloy; silicon-palladium alloy; It is an alloy that is a combination of these (for example, Cu—Ni—Si alloy). Further, the alloy material 16 is a hypoeutectic alloy (that is, a eutectic of silicon A) on the left hand side of the eutectic point EP of the equilibrium diagram 115 in which the weight percent (wt%) composition of the silicon component A is a binary eutectic system. It will be appreciated that the alloy may have a weight percent (wt%) composition of silicon A that is less than the weight percent (wt%) composition. Thus, at any point where the hypoeutectic alloy is present, the concentration of the solute (ie, silicon A) at that point is less than the concentration of the solute (ie, silicon A) at the eutectic point EP. Further, the alloy material 16 is a hypereutectic alloy (that is, a eutectic of silicon A) in which the weight percentage (wt%) composition of the silicon component A is on the right-hand side of the eutectic point EP of the equilibrium diagram 115 of the binary eutectic system. It will be appreciated that the alloy may have a weight percent (wt%) composition of silicon A that is greater than the weight percent (wt%) composition. Accordingly, at any point where the hypereutectic alloy is present, the concentration of the solute (ie, silicon A) at that point is greater than the concentration of the solute (ie, silicon A) at the eutectic point EP. Hypereutectic alloy material 16 is considered to be a multiphase (eg, two-phase) alloy (eg, heterogeneous), while hypoeutectic alloy material 16 is considered to be a single-phase (eg, one-phase) alloy (eg, homogeneous). It is.

The eutectic or hypoeutectic silicon-metal alloy 16 provides resistance to cracking 122 when the cast alloy cools, due at least in part to the substantial absence of silicon microcrystals 120 in the source material 16. (See FIGS. 7a, b). Reduction of cracking 122 can suppress the arrival of ambient air and moisture into the interior of the casting piece 16, thereby reducing oxygen and / or moisture absorption when the cast alloy 16 is exposed to the ambient atmosphere. be able to. This can extend the shelf life of the cast alloy 16. In addition, the release of oxygen or other impurities introduced into the alloy material 16 (due to degradation due to exposure to ambient conditions) into the chlorinated region 12 can be reduced, for example, the process gas 13 Metal-Si alloy material 16 which serves to improve the purity of the chlorosilane mixture in the metal and to help improve the purity of the deposited silicon 27
It will be appreciated that various metal silicon alloy materials may be useful in the apparatus 10 for the production of the carrier gas 15 and the deposition of the silicon 27. For example, nickel silicon, platinum silicon, chromium silicon, and / or iron silicon can be useful alloys, where the metal silicon alloy material 16 has a weight percentage of silicon in the alloy material 16 that is approximately equal to or less than the eutectic composition. Designed to be selected to be It will be appreciated that the weight percent of silicon in the metal silicon alloy material 16 is selected such that the amount of silicon crystallite 120 is below a certain maximum crystallite threshold. Even though any silicon weight percentage in the alloy material above a certain maximum crystallite threshold can be detrimental to the structural integrity of the alloy material due to incompatible / different thermal expansion properties of the crystallite 120 and eutectic matrix 114 It is observed that a sufficient number, size, and distribution of crystallites 120 are introduced. As already discussed, the presence of crystallites 120 in alloy material 16 is detrimental to the structural integrity of the alloy material due to cracks 122, which cracks are sufficient in number, size and above the specified maximum crystallite threshold. This occurs due to the presence of crystallites 120 in the distribution.

  Also, any combination of two or more metals selected from the group in which the metal silicon alloy material 16 includes two or more metals in the matrix 114, such as copper, nickel, chromium, platinum, iron, gold and / or silver. It is also recognized that they can have Furthermore, it will be appreciated that the copper of the metal silicon alloy material 16 may be the largest weight percent of all other alloy components including silicon (eg, for two or more metals).

  Referring to FIG. 6, an example of eutecticity and range for a metallic chromium silicon alloy material 16 is shown.

Example of Cu-Si Alloy Material 16 A further example of alloy material 16 forms a somewhat more complicated phase diagram 115, where at least one eutectic point EP is known (Si is about 16 wt%, Tm = 800 ° C), copper Cu and silicon Si, in which several intermetallic phases are formed. The most prominent among the intermetallic phases is an eta phase made of Cu3Si (having a predetermined phase width depending on the temperature). The melting point of the Cu3Si intermetallic phase is reported to be T = 859 ° C. In the hypereutectic range (eg, the range where the Si concentration is greater than about 16 wt%), copper Cu and silicon Si are fully miscible in the liquid phase throughout the concentration range up to pure silicon Si, but during cooling, the silicon Si is It crystallizes in the form of a dispersed crystallite 120 (needle or plate with a length of a few millimeters), which is buried in the matrix 114 of the eutectic alloy material 16. In the concentration range below the eta phase (ie, the hypoeutectic composition with Si less than about 16 wt%), at least five additional intermetallic compounds are known, most of which have been identified only for the high temperature range. ing.

  In any case, the Cu—Si alloy material 16 is an eutectic alloy material when Si is in the range of about 16 wt%, and hypereutectic when Si is in the range of about 16 wt% to 99 wt%. An alloy material can be defined as a hypoeutectic alloy material when Si is in the range of 1 wt% to about 16 wt%. As described further below, the Cu-Si alloy material 16 for use in the chlorination chamber 12 of the chlorination-deposition system 10Si is, for example, without limitation; 1-16%, 4-16%, 5 -16%, 6-16%, 7-16%, 8-16%, 9-16%, 10-16%, 11-16%, 12-16%, 13-16%, 14-16%, 1 -15%, 4-15%, 5-15%, 6-15%, 7-15%, 8-15%, 9-15%, 10-15%, 11-15%, 12-15%, 13 A silicon crystallite 120 as a silicon other than the matrix / lattice 114 in the alloy material 16 (ie, free silicon) in a weight percent less than the eutectic point EP in the range of -15%, 14-15%, etc. ) Formation or restriction. It is recognized that the crystallite 120 can be considered to be a precipitate that occurs outside of the Cu—Si matrix 114 (ie, excess silicon (greater than about 16% by weight) is insoluble in the Cu—Si matrix 114); Therefore, a crystallite 120 is formed in addition to this matrix 114).

  For example, in the case of a hypoeutectic alloy material 16 of about 12 wt% Si, there is no free silicon (ie, crystallite 120) present in the alloy material 16 or practically close to it. When the wt% of silicon reaches that of the eutectic point EP (eg about 16 wt%), the constituent native silicon can be present up to 4 wt% in the atomic strings, resulting in a homogeneous alloy mixture. Contributes (ie, pure silicon is interspersed within the eutectic structure 114 and thus a homogeneous mixture can be considered a single phase homogeneous mixture). Exceeding wt% (eg, about 16 wt%) of silicon at the eutectic point EP, excess silicon solidifies as pure silicon crystallites 20 and includes a multiphase heterogeneous mixture (ie, eutectic material 114 and silicon crystallites 120). Disperse as one phase of the Thus, an alloy material having a wt% silicon lower than the wt% (eg, about 16 wt%) silicon of the eutectic point EP can be considered a single phase alloy material 16.

  With respect to homogeneity relative to heterogeneity, a homogeneous mixture has one phase, but solute A and solvent B can vary. A mixture is, in a broad sense, two or more substances that are physically in the same position but not chemically bonded, and therefore the ratio is not necessarily taken into account. A heterogeneous mixture can be defined as a mixture of two or more components that can be mechanically separated.

  For example, consider two pure copper alloy materials 16, a first alloy material 16 with a hypoeutectic silicon content of 7% and a second with a hypereutectic silicon content of 22%. The cooling rate of the alloy liquid is low, and it is assumed that equilibrium is established between these phases by short-time diffusion during solidification. The structure of the hypoeutectic alloy material 16 is composed of a fine eutectic Si network scattered in the pure copper matrix 114. In contrast, after the hypereutectic alloy material 16 cools, the material structure consists of the main silicon crystals 120 interspersed as a separate phase from that of the eutectic phase as a matrix 114 containing pure copper and eutectic Si.

  Further, in the case of alloy material 16 containing copper, copper that is atomically combined with silicon or other elements (eg, bonded to silicon in matrix 114) on the outer surface of alloy material 16 The presence of promotes the reaction between the silicon and the injection gas 13 that produces the carrier gas 15 (eg, atomically bonded copper acts as a catalyst for the reaction between the silicon and the injection gas 13). ). Furthermore, since copper is not in a free state (eg, pure copper) but rather in the matrix 114, it can be seen that copper contamination as an impurity in the carrier gas 15 can be suppressed.

Advantages of non-hypereutectic alloy material 16 It is recognized that the alloy material 16 described as hypereutectic is related to the presence of a multiphase alloy having a eutectic material phase 114 and a silicon crystallite 120 (eg, Si crystallite 120). It is done.

  As previously described, with reference to FIGS. 7 a and 7 b, in the case of hypereutectic alloy material 16, large grain size silicon crystallites 120 are scattered throughout the eutectic matrix 114 component / phase of alloy material 16. ing. This heterogeneous multiphase alloy mixture has serious consequences for further use and behavior of the alloy material 16 both inside and outside the chlorination-deposition system 10. For example, during the casting process of the alloy material 16, for example, during the manufacture of the alloy material 16 for later use in the system 10, silicon crystallites 120 are first generated and embedded in the eutectic metal-silicon matrix 114. To do. Silicon crystallite 120 has a different coefficient of thermal expansion compared to eutectic metal-silicon matrix 114, so that the eutectic solidification point during the casting process (eg, Tm = 800 ° C. for Cu-Si). During the cooling of the alloy material 16 from room temperature to room temperature, cracks and microscopic cracks may form in the eutectic metal-silicon matrix 114. These microscopic cracks 122 can lead to progressive oxidation of the cast alloy material 16 unless it is stored, for example, in an inert atmosphere. Under normal atmosphere, the shelf life of the alloy material 16 is limited, and after a period of time can result in the decomposition and collapse of the cast piece of the alloy material 16.

  Furthermore, the increased oxygen level in the hypereutectic alloy material 16 due to continuous oxidation is in the deposited high purity silicon 27 (obtained from the alloy material 16 during the chlorination-deposition process 8). May cause an increase in oxygen concentration. Furthermore, the hypereutectic metal-silicon material 15 may swell (eg, by thermal expansion and / or cracking) during exposure to the inlet gas 13 under normal operating temperatures in the chlorination region 12 of the chlorination process 9. The volume of the alloy material 16 can be increased by a factor of about two. Furthermore, the expansion of the alloy material 16 can result in smaller pieces 124, 126, whereby the physical form of the alloy material 16 is modified into a sponge form, which is a somewhat unstable material form. Can easily collapse (ie, be powdered) upon repeated exposure to the chlorination temperature T associated with the chlorination process gas 13 and the chlorination 9. Swelling / decomposition of the hypereutectic alloy material 16 may further result in the formation of dust and particles 124 in the chlorination-deposition system 10, which may be carried by the gas stream 15 and of the purified silicon 27. May adversely affect purity. In the worst case, the particles 124 can penetrate into the deposited silicon 27 itself. A further disadvantage of using the hypereutectic alloy material 16 is that the poor alloy material 16 can be easily oxidized and powdered due to its sponge form, thereby remelting / reusing. Because it can be difficult to collect.

  For example, with respect to the alloy material 16 embodied as a Cu-Si alloy material, the eutectic or hypoeutectic copper-silicon material 16 suppresses the formation of cracks 122 during cooling of the casting process and the formed eutectic or sub-eutectic material. Oxygen and / or moisture when the eutectic copper-silicon material 16 is exposed to air or other environmental conditions and the oxidant and / or moisture reaches the eutectic or hypoeutectic copper-silicon material 16. The structure of this eutectic or hypoeutectic copper-silicon material 16 is distinguished from hypereutectic alloys in that absorption can be suppressed. This prevention of cracks 122 can extend the shelf life of the casting material 16 and, in the case of a hypereutectic alloy, oxygen that can be trapped in any crack 22 and released during the chlorination process 9. Alternatively, the amount of other impurities associated with process 8 can be reduced.

  In the case of eutectic or hypoeutectic copper-silicon alloy material 16, the lack of buried silicon crystallite 120 (formed in the case of hypereutectic alloy material) has several implications for use in process 9 of the chlorination reactor. With important consequences. When silicon is extracted from the crystallites 120 in the hypereutectic alloy material 16 during the process 9, large voids or cavities 122 (ie expanded cracks 122) are created and the process gas 13 is in the mass of the alloy material 16. It can penetrate. This can lead to swelling / expansion of the alloy material 16 and can cause partial / complete disintegration or powdering of the alloy material 16. This collapse can reduce the filtering effect of the alloy material 16 to control unwanted impurities, further described below, thereby making the purification process 8 of the chlorination-deposition process less efficient. .

  Referring to FIG. 8, the oxidation behavior of the eutectic copper-silicon alloy material 16 (approximately 16 wt% silicon) is compared to the oxidation behavior of the hypereutectic alloy material 128 (40 wt% silicon). Two pieces 16, 128 of similar shaped (8 × 8 × 1.5 cm) alloy material were stored in a normal laboratory atmosphere and the material weight 130 was measured as a function of time 132. A plain copper piece 134 was used as a reference sample. The hypereutectic alloy 128 showed a continuous weight increase representing progressive oxidation. Within about 3 months, a weight gain greater than 1 g was measured, which was about 0.2% of the original total weight of the alloy material 128 (after about 6 to 12 months, the hypereutectic piece 128 is normal Disintegrated and collapsed). At the same time, the eutectic copper-silicon piece 16 does not show any significant weight gain, which can be explained by a solid, crack-free structure of the eutectic material 16.

Formation of Alloy Material 16 Referring to FIG. 12, an example of a casting apparatus 200 used for the manufacturing process of the alloy material 15 is shown, which contains a measured percentage amount of combined metal and silicon. The liquid material 202 is poured into a mold 204 that provides a hollow cavity of the desired physical shape of the alloy material 16. The molten liquid material 202 is then solidified at a controlled temperature to provide the desired eutectic or hypoeutectic matrix 114 of the alloy material 16 (see FIGS. 7a, b / FIGS. 9a, b). In addition, to make the best use of the integral matrix 114 nature of the alloy material 16 (eg, characterized as a polycrystalline structure) and to minimize the formation of crystallites 120 (see FIG. 7a). And control the cooling process. The solidified alloy material 16 is also known as a casting and is either extruded from 205 or removed from the mold 204 to complete the process.

  Referring also to FIG. 13, according to a preferred embodiment, a eutectic or hypoeutectic metal-silicon alloy material 16 is produced by a casting process 220, which is a process for silicon-poor alloy material 16. It can also be modified as a recast process. In this process, silicon, such as m. g. Silicon is melted with a metal (eg, copper) or with a hypoeutectic silicon-copper mixture (eg, a poor alloy material 16). This melting can take place in a graphite crucible or any crucible material that can withstand the silicon-copper melt 202 and does not adversely introduce additional impurities into the melt. The melt 202 is then poured into a mold 204, preferably, but not exclusively, a graphite mold 204 (for example, by shaping the mold 204) of the desired eutectic or hypoeutectic of the defined shape and geometry. An alloy material 16 is formed. In contrast to higher silicon concentration metal-silicon alloys, such as hypereutectic composition, eutectic or hypoeutectic material 16 can be cooled without stress, so a wide variety of shapes (brick, Can be cast into slabs and thin plates. For example, the casting cooling process may be configured to minimize / suppress gas porosity, shrinkage defects, mold material defects, casting material defects, and / or metallurgical / matrix 114 defects. Has been. It will also be appreciated that the physical form / shape of the alloy material 16 may be configured for a fixed bed or fluidized bed reactor (eg, region 12) of the apparatus 10.

  Thus, the alloy material 16 is preferably cast to provide a desired physical form, for example, a selected surface 136 to volume ratio that allows easy loading of the chemical vapor region 12 and exceeds a defined ratio threshold. Provided can be brick, plate, granule, mass, pebble or any other shape.

  In addition, the cast eutectic or hypoeutectic piece 16 may be surface treated before it is used for steam gas production, or they may be used directly. Possible surface treatments include, for example, sand blasting or chemical etching to remove any surface contaminants or any oxide film that may form during the casting process.

  For example, eutectic or hypoeutectic bricks, slabs or plates (or any shape if required) may be used as source material 16 for the production of chlorosilanes in chlorination reactor 12. it can.

Recasting Alloy Material 16 Referring to FIG. 13, (for producing a metal silicon alloy material 16 having a selected weight percent silicon below the eutectic weight percent of silicon defined for each metal silicon alloy). A recast process 220 is shown that is performed after extracting a predetermined amount of silicon from eutectic or hypoeutectic material 16 in process 9 (see FIG. 3). In the case of hypoeutectic and / or eutectic material 16, the alloy material 16 provides its structural integrity thanks to the suppression of crack formation 122 due to the substantial absence (eg, lack) of crystallites 120 present in the alloy material 16. Because it can be retained, the depleted slab, brick or plate or other physical form of the alloy material 16 can be removed from the chlorination region 12. Depending on the purity level required in each of the produced chlorosilane stream 13 or the deposited polysilicon 27, the depleted material 16 is remelted and mixed with additional silicon to produce a chlorination process 9 Unused eutectic or hypoeutectic material 16 may be formed for further use. The number of recycles of the depleted material 16 depends on the threshold for individual impurities and the mg. It can depend on the impurity level of the silicon.

  In step 222, the concentration of silicon in the atomic matrix 114 of the depleted metal silicon alloy material 16 increases from the outer surface 136 of the metal silicon alloy material 16 to the interior 140 of the metal silicon alloy material 16, thereby Melting the poor metal silicon alloy material 16 such that the weight percent of silicon adjacent to the outer surface 136 in the poor material is less than or equal to the hypoeutectic weight percent of the silicon range defined for each metal silicon alloy. To be done. In step 224, silicon (eg, metal grade silicon) is added to the depleted metal silicon alloy material 16 (eg, either in a molten, solid or partially molten form) to obtain the resulting molten material silicon. Is increased to a selected weight percent of silicon below the eutectic weight percent of silicon defined for each metal silicon alloy. In step 226, the molten alloy material is cast to produce a solid metal silicon alloy material 16 suitable for re-generation into the chemical vapor generation region (see FIG. 1) of the apparatus 10. Optional step 228 is a surface treatment of the cast metal silicon alloy material 16.

  It will be appreciated that surface treatment (eg, washing away metal chlorides accumulated on the surface) can be performed on the hypoeutectic alloy. With hypereutectic, this would not be possible due to the formation of a spongy structure, ie, crack 122 as discussed. Depending on the threshold value for impurities contained in the alloy material 16 as a result of the casting process, surface treatment may or may not be performed. Furthermore, oxide and / or carbide slagging-off may be performed as a surface treatment of the alloy material 16 during casting.

Filter Effect of Alloy Material 12 Referring to FIGS. 3, 9a, and 9b, in the case of a hypereutectic alloy material 16 (ie, containing crystallites 120, see FIG. 7a), the swelling of material 16 is a gas The flow of powder and particles from the decomposition of the alloy material 16 (due to expansion / crack formation) may introduce impurities / contaminants into the carrier gas 15 This can contaminate the deposited silicon 27.

  In the case of eutectic or hypoeutectic copper-silicon (ie substantially free of crystallite 120, see FIG. 7a), the piece of alloy material 16 does not swell or appears to change its shape. Nonetheless, it prevents the formation / spreading of the crack 122 and the resulting degradation and / or collapse of the physical integrity of the alloy material 16. Thus, the reaction with the implantation / process gas 13 occurs on the surface 136 of the hypoeutectic or eutectic material 16. Since silicon is known to have a significantly faster agitation rate in copper-silicon than other metal elements, an efficient filter effect can be obtained for any impurities remaining in the alloy material 16. Only these elements (ie, Si in the alloy material 16 or any other possible impurity element) can diffuse to the surface 136 and react with the process gas 13.

  Thus, the matrix 114 can be viewed as a filter or getter of impurities in the alloy material 16 (eg, further in the matrix 114 with copper and silicon), which can be considered as a temperature and other for the carrier gas generation 9. Operating parameters of silicon in a matrix preferential (ie, larger in scale) than the diffusion of possible impurity atoms (eg, Cr, Fe, O 2, N 2, boron, phosphorus, etc.) through the alloy material 16. Because it provides diffusion. Therefore, the matrix 114 acts as a getter / filter during the chemical / metallurgical process of the silicon reaction with the injection gas 13 and absorbs impurities that would otherwise enter the carrier gas 15. The diffusion / migration rate of silicon in the alloy matrix 114 depends on the temperature of the process 9 and / or the concentration gradient of Si in the matrix 114 (for example, the concentration of Si in the matrix 114 depends on the reaction with the injection gas 13. It is also observed that it depends on a number of parameters, such as initial degradation near the surface of the material 16, thereby creating a concentration gradient for silicon in the matrix 114 between the outer surface and the inner surface of the alloy material 16. .

  Atomic diffusion is a diffusion process whereby the random thermal activation of atoms in the solid material 16 results in a net transfer of atoms. The speed of movement depends on the diffusion coefficient and concentration gradient 138. In the crystalline solid state of the matrix 114, Si diffusion within the crystal lattice 114 occurs by either interstitial and / or substitutional mechanisms and is referred to as lattice diffusion. In interstitial diffusion, a diffusing material (eg, Si in a metal-Si alloy) diffuses between the lattice structures of other crystalline elements. In substitutional lattice diffusion (eg, self-diffusion), Si atoms can move by exchanging locations with other atoms in matrix 114. Substitutional lattice diffusion often depends on the availability of vacancies throughout the crystal lattice 114. Due to rapid and essentially random jumps (jump diffusion), the diffusing Si atoms move from vacancies in the matrix 114 to vacancies.

  Since the prevalence of vacancies increases according to the Arrhenius equation, the rate of diffusion of the crystalline solid state can increase with temperature. For a single atom in a defect-free crystal matrix 114, the movement of Si atoms can be explained by a “random walk” model. In three dimensions, it is shown that after n jumps of length α, the atoms will travel on average a predefined distance on average. The atomic diffusion of Si in the polycrystalline matrix 114 material 16 can include a short-circuit diffusion mechanism. For example, there are more open spaces along certain crystal 114 defects such as grain boundaries and dislocations, thereby allowing lower activation energy for diffusion of Si elements. Therefore, atomic diffusion in polycrystalline 114 material 16 is often modeled using an effective diffusion coefficient that is a combination of lattice and grain boundary diffusion coefficients. In general, surface diffusion occurs much faster than grain boundary diffusion, and grain boundary diffusion occurs much faster than lattice diffusion.

  Therefore, silicon moves slower because it is known to have a significantly faster diffusion rate in metal-silicon than other impurity elements (elements that are not desired to be introduced / mixed into the carrier gas 15). The impurity element is trapped in the bulk material 16 and the silicon in the matrix 14 preferentially diffuses to the surface 136 for reaction. In contrast to alloys with excess silicon (i.e. crystallite 120), when elemental silicon from matrix 114 becomes poor, only the Kirkendle voids are predominantly in matrix 114, not large cavities (e.g. cracks 122). Form. The reaction between the surface silicon and the process gas 13 creates a concentration gradient 138, thereby diffusing the silicon in the direction toward the surface 136. Since the amount of lysicon available at surface 136 is defined by the rate of solid state diffusion, the chlorination is such that if the temperature of process 9 is too low, the replenishment of unused silicon at surface 136 will be too low. The temperature T during the process 9 is appropriately selected. If the temperature is too high, with a sufficient amount of silicon, impurities may move through the matrix 114 and may be undesirably included in the carrier gas 15 at a concentration that exceeds a defined impurity threshold. In principle, Process 9 operates at any temperature between 200 ° C. and the melting point of alloy material 16 (eg, for a Cu—Si alloy, eutectic alloy material 16 has a melting point Tmp of about 800 ° C.). can do. For example, 200 ° C. may be an example of a lower temperature boundary where silicon diffusion is below a defined minimum diffusion threshold.

  In the case of the desired metal silicon alloy material 16 (eg Cu—Si), an approximately eutectic or hypoeutectic alloy material 16 is selected for the formation of trichlorosilane or other gas 13 by the heating means 6. Temperature range (for example, 250 ° C-550 ° C, 300 ° C-500 ° C, 350 ° C-450 ° C, 375 ° C-425 ° C, 250 ° C-300 ° C, 350 ° C-550 ° C, 250 ° C-300 ° C, 400 ° C -500 ° C, 400 ° C-550 ° C) and higher temperatures (eg, 450 ° C-Tmp, 500 ° C-Tmp, 550 ° C-Tmp, if silicon tetrachloride or other gas 13 is preferred) 600 ° C-Tmp, 650 ° C-Tmp, 700 ° C-Tmp, 750 ° C-Tmp, 800 ° C-Tmp). The pressure of the process 9 can be in the range of 1-6 bar, for example. In addition, temperature and pressure process parameters can be adjusted to promote / maximize the diffusion of silicon through matrix 114 in other metal silicon alloy material 16 (other than Cu-Si) structures.

Properties of Deposited Silicon 27 Referring to FIGS. 14a, b, purified silicon 27 using eutectic copper-silicon as the source material (12a) and hypereutectic alloy (silicon concentration 30%, 12b). The resistivity is shown. Silicon 27 was deposited on the hot filament by decomposing chlorosilane (ie, trichlorosilane) produced in the chlorinated region 12 by using a hypereutectic or eutectic copper-silicon alloy material 16 respectively. After deposition, the polysilicon rod 27 was cut into sections and the radial resistivity profile 250 was measured with a four-point probe. (Note: Resistivity values greater than 50/100 ohm-cm were 50/100 ohm-cm because this roughly indicates the range to which bulk resistivity can be measured; 50/100 ohm-cm Above this, the effects of surface conditions and grain boundaries become significant.) Eutectic copper-silicon exhibits a much better filter / gettering effect than that of hypereutectic, and a resistivity value of 250 is deposited. Was substantially constant throughout the thickness of the etched silicon 27. On average, a material deposited from a eutectic material has a resistivity that is about an order of magnitude greater than the resistivity of silicon 27 deposited from a hypereutectic material at a selected thickness T location of the material slice. Indicates. (Note: The first 3-4 mm radius has no silicon deposited and is the original filament). Thus, thanks to the filtering effect of the matrix 114 during process 9 at least in part, the resistivity of the deposited silicon 27 is greater than the selected minimum resistivity threshold throughout the thickness of this deposited silicon 27. Are also allowed to remain on top.

Example Operation of Apparatus 10 Referring to FIGS. 3 and 10, an example of a method 230 using the apparatus 10 (see FIG. 3) for purifying silicon is shown, which is: injected gas 13 Reacting with a metal silicon alloy material 16 having a silicon weight percent less than or equal to the eutectic weight percent of silicon defined for each metal silicon alloy; and silicon obtained from the atomic matrix 114 of the metal silicon alloy material 16 Producing a chemical vapor carrier gas 15 containing; flowing 236 the vapor carrier gas 15 through the filament 16 configured to promote silicon deposition; purified from the chemical vapor carrier gas 15 onto the filament Depositing silicon 27 in the form.

  Referring to FIGS. 3 and 11, an example 240 of a method for producing a chemical vapor carrier gas 15 for use in silicon purification by silicon deposition 11 is shown, which example: injection gas 13 for each metal Reacting 242 with a metal silicon alloy material 16 having a silicon weight percent less than or equal to the eutectic weight percent of silicon defined for the silicon alloy; and chemical vapor transport comprising silicon obtained from the atomic matrix 114 of the metal silicon alloy material 16 A step 244 of generating a gas 15; and a step 246 of discharging the vapor carrier gas 15 for use in the subsequent silicon deposition 11.

Example Results of Alloy Material 16 Before and After Process 8 Referring to FIGS. 9a and 9b, a schematic of eutectic copper-silicon piece 16 before and after being subjected to a steam generation process 9 (see FIG. 1). A microscopic structure is shown. In FIG. 9a, after casting, the eutectic copper-silicon alloy material 16 has a uniform composition (eg, a single phase with a homogeneous distribution of silicon in the copper matrix 14). In FIG. 9b, after the extraction of silicon in the chlorinated region 12, the eutectic (or similar in the case of a hypoeutectic composition) remains intact, and the alloy material 16 has been inserted into the region 12 The original shape has not changed apparently. During the extraction of silicon from the alloy material 16, in FIG. 9 a, silicon diffuses through the matrix 14 to the surface 136 of the alloy material 16 where it reacts with the injected gas 13. When the silicon is substantially depleted with respect to the requirements of the vapor generation process, the matrix 14 has a concentration such that the concentration of silicon in the matrix increases from the outer surface of the alloy material 16 to the interior 140 (eg, the central region) of the alloy material 14. The alloy material 16 includes an inherent silicon residue gradient 138.

  The presence of any silicon crystallites in the interior 140 of the alloy material 16 (see FIG. 7a) must diffuse through the alloy material 16 and reach the surface 136 for subsequent interaction with the injected gas 13. There will be no. Therefore, the rate of diffusion of Si originally in the matrix 14 into the surface 136 (eg, matrix diffusion) and the subsequent interaction with the implanted gas 13 is similar to that of Si (eg, crystallites) that were not originally in the matrix 14. 120, see FIG. 7a), it will be appreciated that the rate of diffusion to the surface 136 (eg, material diffusion) and the subsequent interaction with the injected gas 13 will be different. In certain cases, the desired interaction with the Si in the crystallite 120 can preferentially occur due to the decomposition of the alloy material 16 by expansion / crack formation as described above, and thus is not necessarily an alloy material. This is not due to diffusion through 16 (that is, the crystallite 120 in which the crack is buried is exposed to the injection gas 13).

Examples The following examples illustrate the properties and behavior of eutectic and hypoeutectic copper-silicon alloy materials 16 for use in chlorosilane gas 13 production 9 and subsequent production 11 of high purity silicon 27. To do. These are merely examples and are not intended to be limiting in any way, in particular the desired metal silicon hypoeutectic having a defined absence of excess silicon other than the metal silicon matrix 114 (eg, precipitated crystallites 120). And various metals that can be used in the metal silicon alloy material 16 in compliance with the spirit of the eutectic alloy material 16.

Example 1
A eutectic copper-silicon (8 × 8 × 1.5 cm) slab was cast, weighed, and exposed to the atmosphere (conventional laboratory atmosphere). For comparison, a hypereutectic slab having a silicon concentration of 40 wt% silicon and similar dimensions was cast and treated in the same manner as that of the eutectic. As a reference, a pure copper plate was used. The weight of three different pieces was measured over a period of 3 months (see FIG. 8). The hypereutectic alloy slab showed a continuous weight increase over time (after 3 months, the weight increased more than 1 gram and the initial weight of this piece was about 400 g). No significant change was observed with copper-silicon. This indicates that the hypereutectic alloy continuously absorbs oxygen and / or moisture, and the increased amount of weight indicates that continuous oxidation is occurring. The micrograph of the cast hypereutectic alloy slab shows a severe network of microscopic cracks, which provides a large surface for oxidation. Furthermore, it can be assumed that the oxidation leads to a volume change / expansion which causes more cracks and thereby promotes further oxidation. Since eutectic (and even hypoeutectic) materials do not preferentially form microcracks during casting, oxidation can only occur on the surface of the slab 16 itself and penetrate into the bulk of the material 16. do not do.

Example 2
Two atmospheres were exposed to two slabs of eutectic and hypereutectic (30 wt% silicon) composition and no special treatment was applied. After a storage period of about 6 months, the hypereutectic slab lost its integrity and collapsed, and the eutectic slab did not change and apparently maintained its solid structure.

Example 3
A eutectic plate 3 mm thick and 20 × 10 cm long was cast in a graphite mold. This plate could be manufactured without cracks. By way of comparison, similar geometry hypereutectic plates (30 wt% and 40 wt%) always resulted in severe crack formation and breakage due to different thermal expansion coefficients from the crystallites 120 interspersed in the eutectic matrix 114. Caused at least partially by the stress

Example 4
An eutectic slab (brick) measuring 8 × 8 × 1.5 cm was placed in the chlorination reactor (see “Method and Apparatus for Silicon Refinement” application). The total amount of eutectic copper slab was 40 kg and the temperature in the chlorination reactor during the reaction with the process gas was in the range of 300-400 ° C. The produced chlorosilane was sent into the deposition reactor without further purification (see “Method and Apparatus for Silicon Refinement” application). Over a 90 hour period, 4 kg of silicon was extracted from the eutectic slab and deposited on a heated silicon filament placed in a separate deposition chamber. The average deposition rate was 44 g / hour. After deposition, the radial resistivity profile of the deposited polysilicon rod was measured using a four point probe. Throughout the radius, the resistivity is in the range of 100 ohm cm and above, indicating very efficient impurity gettering with eutectic copper-silicon (see FIG. 12a). Throughout the chlorination process, eutectic copper-silicon slabs have no apparent change in their physical shape, and after this process they are completely intact and retain their physical structural integrity. It was.

  As a comparison, a 40 wt% silicon hypereutectic alloy was cast in a similar manner and used in similar chlorination process 9 under similar conditions with respect to temperature and gas composition. The weight of the hypereutectic alloy used was 26 kg. The produced chlorosilane was sent into the deposition process 11 without further purification. A total of 5.4 kg of silicon was deposited, with an average deposition rate of 46 g / hour. The corresponding resistivity profile across the deposited polysilicon radius showed a significantly lower resistivity, especially towards the edge of the slice (FIG. 12b). This reveals that the gettering effect on electrically active impurities (ie boron as confirmed by chemical analysis) is lower in hypereutectic alloys than in eutectics and / or hypoeutectics. It shows. During the chlorination process, the hypereutectic slab swelled and most of it collapsed to form a violent amount of powder.

Example 5
A hypoeutectic slab (Eta phase, 12 wt% silicon) was cast and placed in a chlorination reactor. The temperature during chlorination was in the range of 270-450 ° C. 54 kg of hypoeutectic copper-silicon was used. The produced chlorosilane was sent into the deposition reactor without further purification. Within 117 hours, 4 kg of polysilicon was deposited on the heated filament. The hypoeutectic slab did not change its shape, and the integrity of the slab was completely obtained after the silicon extraction. Neither substantial powdering nor swelling was observed.

  While this invention has been described with reference to illustrative embodiments and examples, this description is not intended to be construed in a limiting sense. Accordingly, with reference to this description, various modifications of the illustrated embodiments, and other embodiments of the invention will be apparent to those skilled in the art. This includes, in particular, any copper-silicon composition of any composition that is close to or in between the eutectic or hypoeutectic composition, although not exactly as described in the embodiments or examples.

  While this invention has been described with reference to illustrative embodiments and examples, this description is not intended to be construed in a limiting sense. Accordingly, with reference to this description, various modifications of the illustrated embodiments, and other embodiments of the invention will be apparent to those skilled in the art. Accordingly, it is contemplated that the appended claims will encompass such modifications or embodiments. Moreover, all of the claims are hereby incorporated by reference into the description of the preferred embodiments.

  Any publications, patents, and patent applications referred to herein are expressly and individually indicated as though each individual publication, patent or patent application was incorporated by reference in its entirety. All of which are incorporated by reference.

Claims (24)

A method for purifying silicon comprising:
Reacting the implant gas with a metal silicon alloy material having a silicon weight percent less than or equal to the silicon eutectic weight percent defined for each metal silicon alloy;
Generating a chemical vapor carrier gas comprising silicon obtained from an atomic matrix of the metal silicon alloy material;
Flowing the vapor carrier gas through a filament configured to promote silicon deposition;
Depositing silicon in purified form on the filament from the chemical vapor carrier gas.   The method of claim 1, wherein the silicon weight percent is in a weight percent range.   The method of claim 2, wherein for the metal silicon alloy using copper as the metal, the weight percent range is from about 8 to about 16 weight percent silicon.   The method of claim 1, wherein the vapor carrier gas comprises chlorosilane and the metal silicon alloy uses copper as the metal.   The method of claim 4, wherein the injection gas comprises hydrogen chloride, hydrogen or a combination of hydrogen chloride and hydrogen.   The method of claim 5, wherein the copper silicon alloy is metal grade silicon.   The method of claim 2, wherein the metal of the metal silicon alloy is selected from the group consisting of: copper; nickel; iron; silver; platinum;   The method of claim 3, wherein the copper silicon alloy comprises about 1 to about 16 weight percent silicon.   The method of claim 8, wherein the silicon-copper alloy comprises about 10 to about 16 weight silicon.   The method of claim 4, wherein the copper silicon alloy material is at a controlled alloy material temperature.   The method of claim 10, wherein the controlled alloy material temperature is between a minimum diffusion threshold temperature and a melting point temperature of the copper silicon alloy material.   The method of claim 10, wherein the controlled alloy material temperature is between about 300 ° C. and about 500 ° C.   A silicon concentration gradient is created between the outer surface of the metal silicon alloy material and the interior of the metal silicon alloy material, and silicon atoms to the outer surface through the metal silicon matrix for consumption by the implanted gas. The method of claim 1, further comprising facilitating diffusion.   14. The method of claim 13, wherein the presence of silicon crystallites in the metal silicon alloy material is less than a defined crystallite threshold.   15. The method of claim 14, wherein the defined crystallite threshold is a property of hypoeutectic weight percent silicon in the metal alloy.   15. The method of claim 14, wherein the defined crystallite threshold is a property of eutectic weight percent silicon in the metal alloy.   The method of claim 1, further comprising the metal silicon alloy material acting as a getter for a defined impurity component present in the metal silicon alloy material.   The method of claim 17, wherein the filtering of the defined impurity component facilitates the production of purified silicon having a resistivity that exceeds a defined minimum resistivity threshold throughout the thickness of the deposited silicon.   19. The method of claim 18, wherein for the deposited silicon, the resistivity at a selected thickness location of the material slice is one or more orders of magnitude greater than the resistivity of the deposited silicon from the hypereutectic alloy material.   The metal silicon alloy material has an affinity for oxidation that is less than a defined affinity threshold, and the material is exposed to an oxidant to promote the retention of structural integrity of the material. the method of.   The method of claim 14, wherein the presence of silicon crystallites in the metal silicon alloy material below a defined crystallite threshold suppresses a reduction in structural integrity of the metal silicon alloy material during exposure to an injection gas. An apparatus for depositing silicon comprising:
A chemistry comprising silicon obtained from the reaction of an implanted gas with a metal silicon alloy material having a silicon weight percent less than or equal to the silicon eutectic weight percent defined for each metal silicon alloy and from the atomic matrix of said metal silicon alloy material A first reactor for generating a vapor carrier gas;
An outlet for flowing the vapor carrier gas through a filament configured to promote silicon deposition;
A second reactor for depositing silicon in a purified form from the chemical vapor carrier gas onto the filament.   A metal silicon alloy material having a silicon weight percent at a selected eutectic weight percent of silicon defined for each metal silicon alloy for use in a chemical vapor deposition (CVP) process, said alloy material A metal alloy material in which the presence of silicon crystallites is below a defined maximum crystallite threshold.   A metal silicon alloy material having a silicon weight percent less than or equal to the silicon eutectic weight percent defined for each metal silicon alloy for use in a chemical vapor deposition (CVP) process.

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